Independent wheel suspension system using thrust bearing constant velocity universal drive joints, bending and torsional motion resistance suspension members and a transversely pivotable differential

ABSTRACT

An independent wheel suspension system having a differential with an output axis therethrough, the differential being coupled to a transverse support tube pivotable about a transverse axis therethrough and by an inboard constant velocity universal joint to a wheel assembly, the wheel assembly being coupled by an arm to a torsion rod carried by the transverse support tube and pivotable about a swing axis through the inboard constant velocity universal joint, whereby the differential is adapted to pivot relative to each of the output, the transverse and the swing axes.

This is a continuation of application Ser. No. 917,426, filed Oct. 10,1986, now U.S. Pat. No. 4,819,756, which is a continuation ofapplication Ser. No. 586,012, filed Mar. 5, 1984, now U.S. Pat. No.4,671,370.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is related to the following copendingapplications assigned to the common assignee hereof:

U.S. Ser. No. 586,086, filed Mar. 5, 1984, entitled "Independent WheelSuspension System Using Thrust Bearing Constant Velocity Universal DriveJoints As Suspension Members", now U.S. Pat. No. 4,611,681;

U.S. Ser. No. 586,056, filed Mar. 5, 1984 entitled "Independent WheelSuspension System Using Thrust Bearing Constant Velocity Universal DriveJoints As Suspension Members In Combination With A Single Prop ShaftJoint and A Transversely Pivotable Differential", now U.S. Pat. No.4,669,571;

U.S. Ser. No. 586,011, filed Mar. 5, 1984 entitled "Independent WheelSuspension System Using Thrust Bearing Constant Velocity Universal DriveJoints As Suspension Members To Minimize Wheel Camber", now U.S. Pat.No. 4,632,203;

U.S. Ser. No. 586,022, filed Mar. 5, 1984 entitled "Independent WheelSuspension System Using Constant Velocity Universal Joints InCombination With A Single Prop Shaft Joint And Mounted Differentials",now U.S. Pat. No. 4,596,299;

U.S. Ser. No. 586,098, filed Mar. 5, 1984 entitled "Independent WheelSuspension Using Thrust Bearing Constant Velocity Universal Drive JointsAs Suspension Members In Combination With A Wheel Assembly AndDifferential Coupled To Pivot About A Transverse Stabilizer", now U.S.Pat. No. 4,600,072; and

U.S. Ser. No. 586,054, filed Mar. 5, 1984, entitled "Independent WheelSuspension System having a Differential Pivotable about Two Axes", nowU.S. Pat. No. 4,705,128.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention pertains to independent wheel suspension systemsand, more particularly, to independent wheel suspension systems whereina constant velocity joint, as an indispensable component of thesuspension system, is combined with a wheel motion resistance suspensionassembly to provide a suspension system for a vehicle wherein thedifferential of the vehicle is pivotable about a first pivot axisestablished on the vehicle frame and a second pivot axis established onthe suspension system.

2. Description of the Prior Art

The present invention has particular application to both front and rearwheel independent suspension systems wherein universal joints are usedto transfer power from a power delivery unit, normally including anengine, transmission and a differential housing, through half-shaftdrive axles to the driving wheels. As a vehicle moves along a roadsurface, the wheels naturally experience an up and down movementrelative to the driving surface. This movement is referred to as jounceand rebound, and the road clearance of various vehicle components varyaccordingly. If the wheels are allowed to move in a plane approximatelynormal to the driving surface, such up and down movements haveheretofore required corresponding changes in the swing length betweenthe wheel and the differential of the power delivery unit. Such changesin swing length are normally effected by allowing an axial adjustmenteither of a driving member relative to the wheels or of one member of adriving member relative to another. Because of the dynamic loadsassociated with these up and down movements of the wheel and thegeometric movements of the suspension members as a result of the variousload and road conditions experienced by the wheels of a vehicle, pastsuspension system design efforts have been directed toward completelyisolating the drive system components from the suspension systemcomponents to prevent the application of suspension loads to the powerdelivery unit or torque translating drive components of a vehicle. As aresult of this approach the structural design criteria of prior artvehicles is to limit the torque translating components of a vehicle tocarry only torque loads to propel the vehicle and to design a separatesuspension system to carry the loads associated with the up and downmovement of the vehicle wheels as a result of load and/or roadvariations.

The foregoing jounce and rebound movements of the driving wheelsrelative to the road surface introduce lateral or axial thrust loadsrelative to the differential of the power delivery unit. The magnitudeof such thrust loads is related to the transmitted torque and to roadprotuberances, cornering speeds, weight distribution, wheel camber, andload carried by the vehicle as well as other factors. Such axial thrustloads have been diverted from the torque translating driving joints byeither suspension control members connecting the wheel assembly to otherpoints on the chassis of the vehicle or by additional structure encasingeither the torque translating half-shaft or driving joints.

Independent wheel suspension systems generally contemplate the use oftwo general types of universal driving joints: the Cardan-type joint andthe constant velocity type joint. The Cardan-type joint consists of twoyokes connected by a plain or rolling type bearing on the ends of aCardan or cruciform-shaped cross. The cross consists of a block and twopins, one pin being smaller than the other and passing through it. Eventhough heat-treated alloy steels are used throughout, the small pindiameters limit the capacity of the joint to carry axial thrust loadsbecause such axial thrust loads normally impose stresses on the pinswhich are multiples of the stresses associated with carrying normaldriving torque. Moreover, the stresses deleteriously augment each otherthrough vector addition. The major deterrent to using a singleCardan-type joint in an independent rear suspension system, however, isthe severe limitation on the allowable angle of articulation under hightorque loads. This is because the velocity ratio of the speed of thedriving to the driven shaft pulsates or "knuckles" with increasingamplitudes as the angular articulation between these shafts increases.The cyclic speed pulsations significantly increase as articulationbetween the driving and driven joint members increase. Such speedpulsations cause correspondingly higher dynamic stresses on the Cardancross pins and corresponding vehicle vibration and noise as loads of anyappreciable inertia are translated through the joint. The higher dynamicstresses wear the joint structure to degeneratively further increase thespeed variations and further limit the ability of the Cardan joint tocarry high torque loads. Moreover, under thrust loads, the normalmanufacturing tolerance of a Hooke's joint or Cardan joint, bythemselves, cause unacceptable vibrations.

To avoid the foregoing deleterious stress and load carrying consequencesof Cardan-type universal joints, their use in vehicles is generallylimited to applications where the normal angular articulation betweenthe driving and driven members is substantially less than ten degrees,usually less than three degrees. Even then, as herein above set forth,other structure is provided to divert the axial thrust loads away fromthe Cardan-type universal joints. For example, British Patent No.765,659 discloses the use of a Cardan-type universal joint to carry justthe driving torque. A spherical socket and a mating ball-shaped memberare provided about the Cardan joint to divert the axial thrust loadsaway therefrom. The patent to Etnyre, U.S. Pat. No. 3,112,8O9, disclosesthe use of Cardan-type universal joints to couple the inboard andoutboard ends of a live axle. Lateral forces on the wheel are disclosedas being resisted by the live axle and also by a cantilever leaf spring.The Cardan universal joints are disclosed as being capable of absorbingaxial loads well in excess of those encountered under normal conditions,but such conditions are limited to use of the joints only as a drivemember and not as a suspension member.

Being limited in their allowable articulation and not being able tocarry axial thrust loads normally associated with an operating vehicle,Cardan-type universal joints are not used as a suspension member,thereby requiring other pivot points displaced outboard from such Cardanjoint and additional suspension control members connected to such otherpivot points to carry the axial thrust loads.

Constant velocity universal joints have heretofore been used withindependent wheel suspension systems to avoid the debilitating effectsof the foregoing cyclic speed variations of Cardan-type joints whilepermitting substantially greater articulation angles of the wheel withrespect to the drive shaft or the drive shaft with respect to thedifferential of the power delivery unit. Constant velocity universaljoints of the type that provide uniform velocity between the driving anddriven members at any intersecting angle of the joint are shown in U.S.Pat. No. 2,046,584 to Rzeppa, U.S. Pat. No. 3,162,026 to Ritsema, andalso commonly assigned U.S. Pat. Nos. 3,688,521, 3,928,985, 4,240,680and 4,231,233, the specifications of which are hereby incorporated byreference. However, such known constant velocity universal joints haveheretofore been used to carry just the driving torque transmittedthrough the spherical ball members of the joint. These balls ride insets of opposing axial grooves formed on a partially-spherical innerjoint member and on a partially-spherical outer joint member. Ball guidemeans, in the form of a cage, are positioned to capture and guide theballs through a homokinetic plane of rotation wherein the centers of theballs very nearly bisect the articulation angle between the sphericalsurfaces of the outer and inner joint members resulting in a constantvelocity transmission of rotary motion. The ball cage normally consistsof upper and lower partially-spherical surfaces guided, respectively, onthe partially-spherical inner and outer surfaces of the joint members,but are designed to have radial clearances therebetween in order toensure lubrication of the surfaces and thereby avoid excessive heatbuild up.

As explained more fully in the aforesaid U.S. Pat. No. 3,928,985, issuedDec. 30, 1975, when the connecting drive shafts transmit torque loads atan articulated angle, internally generated joint friction and jointgeometry of such constant velocity universal joints cause the inner andouter joint members to shift with respect to each other to take up theaforementioned clearances. Balls in diametrically opposite sets ofgrooves are thrust in opposite directions, causing the cage to besomewhat tilted or skewed relative to the design. The forward and aftend portions of the upper and lower partially-spherical surfaces of thecage are tilted or skewed under torque transmitting loads and bearradially against the inner and outer spherical joint members. Suchskewed contact between the inner and outer spherical surfaces of thecage with the respective inner and outer joint members is tolerated toavoid the undesirable friction effects of greater surface contacts withsmaller clearances. The internally generated loads, as a result oftorque transmission through the joint, have been observed to decreasefrom about a maximum of three hundred pounds per wheel, which occurswhen maximum torque is transmitted at extreme articulation angles of thedrive joints just before a vehicle begins to move.

In any event, the balls and axial grooves of the constant velocityuniversal joint have heretofore been used to translate the drivingtorque while the spherical portions of the inner and outer joint membersexperience the internally generated loads, such internally generatedloads being carried either by direct contact between the inner and outerjoint members or through the interposed spherical surfaces of the cage.As taught in U.S. Pat. No. 3,789,626, to Girguis, where one constantvelocity universal joint was used as a fixed joint, as in the driveshaft of a rear drive motor vehicle, an object of such an application isto maintain the joint elements free of axial internal forces, eventhough the joint was constructed to absorb forces, at least thoserelated to torque translation. In fact, the joint was designed to avoidtransmitting axial forces through the control element. Therefore, whenused at opposite ends of a driving half-shaft, one of such constantvelocity universal joints has heretofore been of the axial slip orplunging variety, allowing axial movement of the driven joint withrespect to the driving joint, and the constant velocity universal jointat the other end has been of the non-axial slip or fixed type notpermitting such axial movement.

In any event, such constant velocity joints and the drive shaft thatcouple them have heretofore not been used to transmit anything more thantorque loads, and the related internally generated axial loads. Forexample, U.S. Pat. No. 3,709,314, to Hickey, discloses the use of aRzeppa or Bendix-Weiss type of constant velocity joint at both ends ofeach of two front-wheel drive shafts, and a Rzeppa type constantvelocity joint is disclosed at both ends of each of two rear-wheel driveshafts. Hickey further discloses four suspension units of the typeconventionally used to divert externally generated axial thrust loadsaway from the constant velocity universal joints. The suspension unitsare substantially similar, except for variations in torsion bar, shockabsorber and linkage attachment points due to the location of the units,front to rear and side to side. Each typical suspension unit isdisclosed as consisting of a conventional upper A-frame arm and lowerA-frame arm. These are connected to tubular frame members by means ofmultiple brackets permitting vertical swinging motion. The wishbone endsof the A-frame arms are shown pivotably connected forward and aft of thecenter of each wheel, and in no instance is any drive shaft shown ordisclosed as being any part of the suspension system or being a part ofa typical suspension unit. U.S. Pat. No. 3,625,300 to Barenyi, et al.,discloses the suspension of an axle unit of a motor vehicle by a supportmember permitting pivoting of the wheel pair in relation to the vehiclesuperstructure about two mutually perpendicular essentially horizontalaxes, but without allowing any relative movement about either axisbetween the wheels and the axle gear housing.

SUMMARY OF THE INVENTION

The present invention recognizes and utilizes the fact that once aconstant velocity universal joint is used as one of an at least two partindependent wheel suspension system, the second part may be coupled tothe vehicle frame in a manner affording new and improved concepts forresisting wheel motion while also affording new and improved conceptsfor supporting a vehicle differential to increase road clearance andtrunk space.

The present invention contemplates the use of a constant velocityuniversal joint at least at the inboard end of a wheel drive shaft so asto function as one essential and indispensable suspension or componentpart of an independent wheel suspension system pivotable about both thejoint axis and the drive shaft axis. A second essential andindispensable suspension part of the independent wheel suspension systemconsists of a transverse support structure mounted to the vehicle frameso as to allow a transverse bending or pivoting motion about atransverse support axis defined therethrough. The second suspension partfurther includes wheel motion resistance means mounted to the transversesupport structure and pivotable at the inboard constant velocityuniversal joint about a swing axis therethrough to allow longitudinalbending or pivoting. The second suspension part of the independent wheelsuspension system resists both the transverse and longitudinal pivotingor bending motion about the respective transverse and swing axes.

In one embodiment of the invention, the wheel motion resistance meansinclude a longitudinal torsion rod and a swing arm. The longitudinaltorsion rod has a fixed end secured to the vehicle frame and a torsionend pivotably supported by the transverse support structure. The swingarm has a wheel end connected to the vehicle wheel and a torsion rod endpivotally attached to the transverse support structure. The swing armand the longitudinal torsion rod cooperate to resist both thelongitudinal bending motion about the swing axis and also thelongitudinal bending motion about the transverse support axis.

A further feature of the present invention is the pivotal mounting ofthe vehicle differential to the transverse support structure by mountingmeans connected therebetween, thereby allowing the differential to pivotabout the wheel drive axis as the axis of the transverse supportstructure moves up and down in response to movement of the vehicle framewhile at the same time being able to pivot about the transverse supportaxis as the wheel drive axis moves up and down. Such mountingarrangement increases the road clearance and trunk space compared toconventionally-mounted differentials.

It is a primary object of the present invention to provide a new andimproved independent wheel suspension system.

It is another primary object of the present invention to provide anindependent wheel suspension system having at least two essential andindispensable parts, the first part having the wheel drive shaft and atleast an inboard constant velocity universal joint capable ofwithstanding axial thrust loads along the wheel drive axis and thesecond part having motion resistance means for resisting motion aboutboth a swing axis through the inboard constant velocity universal jointand also a transverse support axis.

It is another primary object of the present invention to provide anindependent wheel suspension system having a differential pivotableabout more than one axis.

It is another object of the present invention to provide an independentwheel suspension system of the foregoing type wherein the wheel motionresistance means includes a transverse support structure, torsion rodassembly, and swing arm means, the transverse support structure beingpivotably mounted to the vehicle frame to define a transverse supportaxis, the torsion rod assembly having a torsion end pivotably supportedby the transverse support structure, and the swing arm means couplingthe vehicle wheel and the torsion end of the torsion rod assembly.

It is another object of the present invention to provide an independentwheel suspension system wherein the differential of the power deliveryunit is mounted to the transverse support structure so as to bepivotable with respect to the wheel drive axis as well as the transversesupport axis with motions of the vehicle frame about either thetransverse or swing axes.

It is a further object of the present invention to provide anindependent wheel suspension system of the foregoing type wherein thedifferential of the power delivery unit is suspended from the vehicleframe in a manner increasing road clearance while increasing availabletrunk volume.

It is a further object of the present invention to provide anindependent wheel suspension system in which the differential of thepower delivery unit is suspended about the transverse support axis andwheel drive axis so as to reduce the bend angle at the prop shaft joint.

It is a further object of the present invention to provide anindependent wheel suspension system wherein simple spring systems can beused.

It is a further object of the present invention to provide anindependent wheel suspension system to replace carriers that wouldotherwise be necessary to thereby reduce the unsprung mass andproduction costs.

It is a further object of the present invention to provide anindependent wheel suspension system that forms a single assembly unit.

It is a further object of the present invention to provide anindependent wheel suspension system that isolates and dampens noise, andreduces suspension harshness and vibrations related to the powerdelivery unit.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features and objects of the invention will become moreapparent to those skilled in the art from the following detaileddescription of a preferred embodiment taken in conjunction with thedrawings wherein:

FIG. 1 is a schematic view of an independent wheel suspension systemincluding at least two suspension parts, the first part of whichincludes constant velocity universal joints at both the inboard andoutboard ends of the drive shaft connecting the power delivery unit tothe driving wheels and the second part of which includes vehicle motionresistance mean coupling each wheel to the vehicle frame;

FIG. 2 is a plan view of an independent wheel suspension system providedin accordance with the present invention;

FIG. 3 is a view, partially isometric and partially in cross-section, ofa bushing coupling the transverse tube, torsion rod, and swing arm inaccordance with the present invention;

FIG. 4 is a view, partly in cross-section, of one type of constantvelocity universal joint suitable for use as the first part of theindependent wheel suspension system;

FIG. 5 is a side view taken along line 5--5 of FIG. 2;

FIG. 6 is a diagrammatic side view of the independent wheel suspensionsystem of the present invention positioned in a normal, fully loaded,and a totally unloaded position; and

FIG. 7 is a diagrammatic side view of the independent wheel suspensionsystem provided in accordance with the present invention showing theincreased ground clearance afforded thereby with respect to aconventional independent wheel suspension system.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to the drawings, there is shown in FIGS. 1 through 7 afour-wheeled motor vehicle which includes a body 5 mounted to a chassis10. The chassis 10 is supported in a known manner, such as by springs orshock absorbers (not shown), with respect to a chassis support means inthe form of a vehicle frame 12 consisting of a first longitudinal framemember 14 and a second longitudinal frame member 16, and at least onetransverse support member spaced therebetween and suitably affixedthereto. Chassis and/or chassis support means, as used herein, areintended to include a vehicle made of unitary construction wherein someof the chassis components are provided in the body of the vehicle. Thetransverse support member is shown in the form of a transverse tube 18,as shown in FIG. 2, the outboard ends of which are rotatably supportedby bushings 20 and 21 carried by the first and second longitudinal framemembers, 14 and 16 respectively, so as to permit a rotatable motionabout a transverse axis 19 coaxial with the axis of the transverse tube18.

A differential 24 of a power delivery unit is suspended from thetransverse tube 18 by differential mounting means in the form of amounting plate 26 having a rear end 28 secured to the differential 24 bysuitable means, such as bolts 30. The front end 32 of the differentialmounting plate 26 terminates in a partly curved lip 34 suitable affixedto the periphery 36 of the transverse tube 18 by suitable known meanssuch as welds 38, as shown in FIG. 5. Coupled to the input end of thedifferential 24 by a universal coupling such as a Hooke's or Cardanjoint 40 is the drive end 42 of a prop shaft 44, as better seen in FIGS.5 and 6, the prop shaft 44, in turn being coupled by another universaljoint 47 to a source of drive power, such as an internal combustionengine (not shown). The prop shaft 44 operates in a known manner totranslate driving torque about a prop shaft axis 45, locatedintermediate the first and second longitudinal frame members 14 and 16,from the engine to the differential 24, which redirects such drivingtorque to the lateral half-shaft assemblies about a respectivedifferential output axis 25.

As more fully set forth in U.S. Pat. No. 4,611,681, the specification ofwhich is hereby incorporated by reference, the vehicle further includesan independent wheel suspension system for each driving wheel assembly58. Each such independent suspension system consists of at least a firstsuspension part 52 and a second suspension part 54 for independentlysuspending each driving wheel assembly 58 with respect to a drivingsurface 56 through a respective wheel assembly. Each such firstsuspension part 52 has an inboard constant velocity universal joint 60coupled by a half shaft or drive shaft 62 to an outboard constantvelocity universal joint 64. The inboard constant velocity universaljoint 60 is mounted to a lateral side of the differential 24 by suitablemounting studs 46, and the outboard constant velocity universal joint 64is mounted to the wheel assembly 58 for rotatably driving the drivingwheels 50 about a wheel axis 51, as shown in greater detail in U.S. Pat.No. 4,231,233, issued Nov. 4, 1980, the specification of which is herebyincorporated herein by reference.

Each inboard and outboard constant velocity universal joint 60 and 64 ispreferably of the fixed, or non-axial movement type, as shown in greaterdetail in FIG. 4, and includes an inner and an outer joint membercoupling respective shafts having therebetween an angular intersectionA, also known as the articulation angle. The articulation of theassembly is normally on the order of three to six degrees when thevehicle is at rest, but under full load of the vehicle, as well asconditions of wheel jounce and rebound, may be on the order of ten tofifteen degrees or more.

In certain applications, one or both of the inboard and outboardconstant velocity universal joints 60 and 64 may also be of the axiallyplunging, telescoping, or splined types, such as those shown in U.S.Pat. No. 3,688,521, to Smith, et al., issued Sept. 5, 1972, thespecification of which is hereby incorporated herein by reference, aslong as the universal joint of any such type, at either end of theiraxial travel, function as a suspension part of the independent wheelsuspension system in the same manner as a fixed constant velocityuniversal joint. Moreover, some applications may require that only theinboard joint be of the constant velocity universal type, the outboardcoupling being of another type, universal or otherwise.

Each second suspension part 54 includes a wheel motion resistanceassembly in the form of a swing arm 70, and a torsion rod 72 cooperatingwith the transverse tube 18. Each swing arm 70 has a wheel end 74 and atorsion rod end 76. The wheel end 74 is pivotably connected to the wheelassembly 58 such as by a pivot knuckle 80, and the torsion rod end 76has an axial length section 82 with a hexagonally-shaped socket 84therein for capturing a hexagonally-shaped end 86 of the torsion rod 72.The other end of the torsion rod 72 is suitably captured and securedboth axially and circumferentially to a forward frame end 13 of thevehicle frame 12 in a suitable known manner, such as by anotherhexagonally-shaped socket and bolt arrangement 88. As best seen in FIG.3, each torsion rod 72 is pivotally journalled in a annular rod bushing92 suitably fixed to the transverse tube 18 such a by mounting grommets94 and 96 having flats 98 to prevent circumferential slippage. The firstand second suspension parts 52 and 54 swing, or pivot, about a swingaxis 53 developed by the longitudinal axis of the torsion rod beingaligned with the homokinetic center of the inboard constant velocityuniversal joint 60. The first and second suspension parts 52 and 54 alsopivot about the transverse axis 19. But the tendency to pivot about eachof these axes is resisted and dampened by the foregoing wheel motionresistance assembly in a manner made more apparent from the followingdescription of the operation.

OPERATION

The operation of the independent wheel suspension system of the presentinvention may be better understood with reference to the three driveline positions shown in FIG. 6. Therein, position I represents thestandard normal condition wherein the only load on the vehicle inaddition to its weight, as delivered, is the average weight of anaverage driver. The prop shaft 44 has a slight upward inclination fromthe engine to the differential 24 and the differential 24 has a slightdownward inclination rearwardly from the transverse axis 19 to thedifferential output axis 25. Position II represents the fully-loadedcondition wherein the vehicle is loaded with the equivalent of fivepassengers in the passenger compartment and appropriate weights of threehundred pounds in the trunk. Position III represents the standardunloaded condition in which the vehicle frame is raised from the grounduntil the wheels just lift off or freewheel. The independent wheelsuspension system is designed so that all other normal conditions,including jounce, rebound and cornering, effect positions intermediatepositions I, II, and III.

In obtaining the fully loaded position II, the vehicle frame 12 and thetransverse tube 18 are moved downwardly toward the road surface 56, intothe plane of the paper as viewed in FIG. 2, or downwardly in a directiontoward the road surface 56 illustrated in FIGS. 5 through 7. Assumingthere is no jounce or rebound of a driving wheel 50 relative to thedriving surface 56, each driving wheel 50 tends to swing upward relativeto the vehicle frame 12 about both the transverse axis 19 and the swingaxis 53. But, this motion is resisted and dampened by the torsion rod 72through the swing ar 70. The upward movement about the swing axis 53 isresisted by the torsional stiffness of each torsion rod 72 and theupward movement about the transverse axis 19 is resisted by thelongitudinal bending stiffness of each torsion rod 72.

Because the differential is pivotable about the transverse axis 19, aswell as about the differential output axis 25, the differential 24 movesdownward relative to the driving surface 56 by a designed proportion,preferably less than one third of the downward movement of the vehicleframe 12 at the transverse tube 18 relative to the driving surface 56.The exact differential-to-frame movement ratio is determined by variousparameters including desired spring rates, normal and extreme angles ofarticulation, lateral axial loading through the inboard constantvelocity universal joint, the length of the swing arm 70, desired trunkvolume and, of course, desired minimum road clearance. For example, ifdesigned to normally effect a slight downward or articulation of atleast three degrees from each inboard constant velocity universal joint60 out to each driving wheel 50, the driving wheel 50 will normallyexert an upward axial force on the inboard constant velocity universaljoint 60 through the drive shaft 62. Such upward force tends to maintainthe prop shaft center of the differential 24 in its normal position Ieven though the forward end of the differential 24 pivots downwards,clockwise in FIG. 6, about the wheel axis 51 as the forward end of thedifferential 24 follows the downward movement of the transverse tube 18.

As the vehicle travels down a flat driving surface 56, being normallyloaded, such as with just a driver, the independent wheel suspensionsystem is configured so that the differential output axis 25, which iscoincident with the axis of the driving member of the inboard constantvelocity universal joint 60, is located horizontally above the wheelaxis 51 of the driving wheel 50, as shown in FIG. 5. This offset iseffected by an upward articulation angle of three or four degreesbetween the inner and outer members of each constant velocity universaljoint. Moreover, the suspension system is configured to afford a slightrearward tilting of the vertical axis 22 of the differential 24counterclockwise, as viewed in FIG. 5, from the normal axis 55 to thedriving surface 56. This slight rearward tilt of the vertical axis 22 ofthe differential 24 about the transverse axis 19 is increased, as betterseen in FIG. 6, as the driving wheel 50 moves downward relative to thetransverse tube 18, so that the differential 24 and the prop shaft 44move toward the unloaded upward position III relative to the normalposition 1. For example, should the driving wheel 50 move downwards orinto the plane of the paper as viewed in FIG. 2, such as by droppinginto a road pothole, such downward movement would be resisted by thecooperation of the torsion rod 72 with the swing arm 70 about the swingaxis 53. Moreover, such downward movement would also be resisted by thebending resistance about the transverse axis 19 imparted to the torsionrod end 76 of the swing arm 70 by the bending of the torsion rod 72.

The annular rod bushing 92 and the bushing cup transfer to thetransverse tube 18 the longitudinal bending resistance of the torsionrod 72 to further restrain both the downward movement of the drivingwheel 50 about the transverse axis 19 and also the downward movement ofthe differential 24 thereabout through the differential mounting plate26 being attached to the transverse tube 18.

Conversely, when the wheel travels over a bump, the drive train assumesthe fully loaded downward position 11 with respect to the normalposition I wherein the vertical axis 22 of the differential 24 ispivoted forwardly through the normal axis 55 to the driving surfaceabout the transverse axis 19 of the transverse tube 18.

As may be better understood with reference to FIG. 7, the foregoingindependent wheel suspension system provides a road clearance C betweenthe bottom edge 23 and the driving surface 56 when the driving wheels 50go over a bump. Such clearance C has been determined to be at leasttwice the clearance D afforded between the conventional independentwheel suspension system and the driving surface 56. This largedifference results from the fact that in a conventional independentwheel suspension system the differential is mounted directly to theframe rather than being pivotably connected thereto in accordance withthe teachings of the present invention. In a conventional independentwheel suspension system, the differential is mounted directly to a rigidframe member and moves up and down therewith, reducing the normal groundclearance to D as the vehicle is loaded towards the fully loadedposition 11, or a wheel goes over a bump, or both. However, with thepresent invention, loading of the vehicle to the fully loaded positionII results in a forward pivoting of the differential 24 about thetransverse axis 19 and differential output axis 25 due to the forwardbending movements about the transverse axis 19 of the transverse tube 18imposed thereon by each driving wheel 50 through the swing arm 70.

Even though the differential 24, therefore, swings about the transverseaxis 19, the linear motion of the differential 24, relative to thedriving surface 56, is only a predetermined portion of the linear motionof the frame 12 relative to the driving surface 56. Therefore, inaddition to affording greater road clearance C, the independent wheelsuspension system of the present invention also affords greater trunkclearance between the top 27 of the differential 24 and the bottom ofthe trunk 29 as well as narrower or smaller drive shaft tunnels (notshown).

While the wheel motion resistance means consisting of the secondindependent wheel suspension part 54 includes, in the preferredembodiment, a swing arm 70 and a longitudinal torsion rod 72, it will beapparent to those skilled in the art that other wheel motion resistancemeans may be employed as long as the differential 24 is allowed to pivotabout the transverse axis 19 and the differential output axis 25. Forexample, the resistance to longitudinal bending provided by the torsionrods 72 could also be supplied by equivalent means, such as an hydraulicleveling and/or dampening device or coil spring acting at appropriatepoints of either the differential mounting plate 26 or the wheelassembly 58.

Moreover, it is also apparent that the swing arm 70 may be affixed toother portions of the torsion rod 72, such as forward of the transversetube 18, as for example shown in U.S. Pat. No. 4,669,571, thespecification of which is hereby incorporated herein by reference.Moreover, as will also be apparent to those skilled in the art, themotion resistance means may also include various combinations of helicalsprings, leaf springs, shock absorbers and other known suspensiondevices.

Although the best mode contemplated for carrying out the presentinvention as of the filing date hereof has been shown and describedherein, it will be apparent to those skilled in the art that variousmodifications and variations may be made without departing from what isregarded as the scope of the invention.

What is claimed is:
 1. An independent wheel suspension system for awheel assembly of a vehicle having vehicle support means for supportinga vehicle chassis, said independent wheel suspension systemcomprising:transverse support means supported by said vehicle supportmeans so as to be pivotable about a transverse axis; power deliverymeans fixedly connected to said transverse support means and having anoutput axis and an inboard constant velocity universal joint adapted tocarry lateral thrust loads along said output axis; pivot means carriedby said transverse support means so as to be pivotable about asubstantially longitudinal swing axis through said inboard constantvelocity universal joint; and arm means coupling said wheel assembly andsaid pivot means for allowing said power delivery means to pivotrelative to at least two axes of said output axis, said transverse axis,and said longitudinal swing axis.
 2. The independent wheel suspensionsystem of claim 1, wherein said power delivery means is allowed to pivotrelative to the other of said output axis, said transverse axis, andsaid swing axis.
 3. The independent wheel suspension system of claim 1,wherein said transverse support means is adapted to have a displacementbetween a normal position and a fully loaded position and said powerdelivery means is adapted to move a predetermined portion of saiddisplacement.
 4. An independent wheel suspension system for a vehiclehaving a power delivery unit for translating torque from an enginethrough a differential to a vehicle drive wheel in contact with adriving surface, said independent wheel suspension systemcomprising:transverse support means mounted to said vehicle so as topermit movement of said transverse support means relative to saidvehicle, said transverse support means having a first axis of rotation;a second axis of rotation extending substantially parallel to said firstaxis of rotation and spaced in a predetermined position relative to saidfirst axis of rotation for cooperation therewith; and means for fixedlymounting said differential to said transverse support means and aboutsaid second axis of rotation such that said differential pivots aboutsaid first axis of rotation with said transverse support means when saidvehicle drive wheel is displaced relative to said vehicle and about saidsecond axis of rotation when vehicle is displaced relative to saiddriving surface.